only to possess freedom from additional errors, but to give better results or 

 as good results as two different and separate instruments at less cost of con- 

 struction, less weight for transportation and mounting, and greater rapidity of 

 manipulation. For certain classes of work, the universal instrument has, with- 

 out doubt, some decided advantages; but for such work as is demanded in the 

 primary and main triangulation of the United States they are essentially un- 

 suited. Nor would our surveys willingly adopt the eccentrically placed tele- 

 scopes of the theodolites used in the Prussian Geodetic Survey, although the 

 character of that wcrk stands very high; if any series of observation is broken 

 it cannot be utilized without extra calculation; and a loss of time means a loss 

 of money. The multiplicity of parts in some of the instruments on exhibition 

 was astonishing. I was attracted by the complication of an instrument having 

 a circle of about eight inches diameter, and although I could see little more 

 than one side of the instrument I counted no less than 93 screws of all kinds, 

 whilst others seemed evolved and contrived from the inner consciousness of 

 some closet professor. 



In one large combination instrument in the exhibition, there were, among 

 other curious features, two small lamps for illuminating the horizontal circle 

 under the three microscopes; one for the telescope, and one for reading the 

 level and the two microscopes for the vertical circle, together with a multipli- 

 city of mirrors to reflect the lights. No matter howsoever small the heat ot the 

 flames might be, here was the introduction of souces of error that wou'd tend 

 to complicate and mask the other defects of the instrument. 



I had the opportunity of studying many of the recent and varied forms of 

 portable transit instruments. Some there were that never should have been 

 permitted to leave a workshop; others aiming at great stability by the use of very 

 heavy cast-iron stands, yet introducing an element of error in having their ad- 

 justments for level and azimuth at the base. This seems very much like 

 erecting a great solid building upon a movable foundation. It is granted that 

 in the usual form of movable Y's tor the adjustment of the transit axis level 

 and of azimuth, two fertile sources of error exist, but many years since I 

 readily and successfully overcame the difficulty by tightly clamping either mov- 

 able Y alter the last mechanical correction has been made to the adjustments. 

 Troughton and Simms have in part since used a similar application. The frames 

 of the later Coast Survey transit instruments are emphatically portable from 

 their form and weight of metal ; their telescopes have generally greater light- 

 collecting power than the portable transits examined, whilst the character of 

 the results is fully established by the rigorous method of discussing them. By 

 the adoption of four foot-screws 1 have secured remarkable firmness; whilst the 

 double frame gives no ,only great facilities for preliminary adjustments in the 

 meridian, but enables the trans" t to be used for a latitude instrument by the 

 Talcot method. Some of the portable transits in Europe hardly bear out that 

 character, and would not be adopted in the mountains where our geodetic 

 work is being carried; it was very evident that cast-iron was cheap, transpor- 

 tation easy, and time no object. And I found severer criticisms than mine 

 passed upon particular instruments (designed for great surveys) by some whose 

 opinions have much weight in the geodetic world; whilst one well known 

 observer confessed, that were he to design a new instrument it would not have 

 the form of that which he had planned, constructed and already used. 



Although I made few efforts to examine the manufacture of lenses for tel- 

 escopes and microscopes, those which I did see were generally of superior 

 character. I was very much impressed with the thorough skill and knowledge 

 of Shroeder, of Hamburg, who was making the lenses for the 15-inch equa- 

 torial of the new Potsdam observatory. An examination of some of his smaller 

 instruments revealed marvelous precision of figure, whilst his means of testing 

 the curvature of the lens was beyond anything I had seen or known. The 

 computations for the curvatures of the lenses are very elaborate and exhaustive. 



Without going into details of telegraphic longitude apparatus, electrical 

 clocks and chronometers, etc., I may mention that I examined the base ap- 

 paratus of Brunner, being constructed for the Spanish Geodetic Survey; and 



